Process for catalytic reforming with high propane yield

ABSTRACT

An improved hydroforming process wherein the n-paraffins in the hydroformer feed are converted to normally gaseous hydrocarbons, particularly propane. The improvement is accomplished by placing a selective hydrocracking catalyst comprising hydrogen-erionite in the bottom of the lead reactor of a multiple-stage, fixed-bed hydroforming process. The normally gaseous hydrocarbons are separated from the lead reactor effluent. The propane yield can be maximized, and the octane rating of the hydroformer product is improved.

United States Patent 72] Inventors Maurice G. Lorenz Baton Rouge, La.; Charles Kirk Brown, Florham Park, NJ. [2]] Appl. No. 791,487 [22] Filed Jan. 15, 1969 [45] Patented Nov. 2, 1971 [73] Assignee Esso Research and Engineering Company [54] PROCESS FOR CATALYTIC REFORMING WITH HIGH PROPANE YIELD 5 Claims, No Drawings [52] US. Cl.. 208/66 [51] Int. Cl ..Cl0g 35/04, C lOg 39/00 [50] Field of Search 208/65, 66, l l l [56] References Cited UNITED STATES PATENTS 3,114,696 l2/l963 Weisz 208/66 3,392,107 7/l 968 Pfefferle 3,395,096 7/1968 Gladrowetal.

Primary ExaminerDelbert E. Gantz Assistant Examiner-R. Bruskin Anomeys- Pearlman and Stahl and Wayne Hoover ABSTRACT: An improved hydroforming process wherein the n-paraffins in the hydroformer feed are converted to normally gaseous hydrocarbons, particularly propane. The improvement is accomplished by placing a selective hydrocracking PROCESS FOR CATALYTIC REFORMING WITH HIGH PROPANE YIELD BACKGROUND OF THE INVENTION This invention relates to a method for increasing the production of normally gaseous hydrocarbons during a hydroforming operation. More particularly, this invention relates to a method for selectively converting the n-paraffins in a hydroformer feedstock to lower molecular weight, normally gaseous hydrocarbons. Still more particularly, this invention relates to a hydroforming process wherein a selective hydrocracking catalyst is used in combination with a hydrofonning catalyst in the lead reactor of a fixed-bed hydroforming process. Still more particularly, this invention relates to a hydroforming process wherein a hydrocracking catalyst comprising hydrogen-erionite is used in the lead reac- IOI.

Hydrofonning is a well-known, widely used process for upgrading hydrocarbon fractions boiling in the motor gasoline or naphtha boiling range to increase the octane number and to improve their burning or engine cleanliness characteristics. These improvements are due largely to the conversion of naphthenes to aromatics, although a variety of other conversion reactions do occur during the hydroforming operation.

It is known in the prior art that the n-paraffin content of a hydroformer feed is not easily converted to higher octane materials. Accordingly, the presence of n-paraffins in a hydroformer feed operates to limit the potential improvement which can be realized from the hydroforming operation. Moreover, it is also known that the presence of n-paraffins in the hydroforrner feed leads to undesirable side reactions, such as coking, which accelerates the deactivation of the hydroforming catalyst.

Several methods for avoiding the problems associated with the presence of n-paraffins in the feed have been disclosed in the prior art. Moreover, in copending application Ser. No. 637,91 l, filed May 12, I967, thereis disclosed a method wherein the hydroformer feed is treated to convert the nparaffins to branched-chain hydrocarbons or to lower boiling materials which are easily removed from the feed. In application Ser. No. 637,9l 1, this conversion is accomplished by first contacting the hydroformer feed with a 4 to 6-Angstrom zeolite containing a metal cation selected from the Group "-8 metals. In this case, the C and lighter hydrocarbons are preferably removed from the feed before it enters the lead reactor of the hydroformer train.

The principle disadvantage of the prior art processes is that separate facilities for the reaction and catalyst regeneration are required for both the pretreating and hydroforming steps. This, in turn, gives rise to a higher initial investment and higher operating costs which distract from the commercial attractiveness of the processes.

BRIEF SUMMARY It has now been found that the foregoing and other disadvantages can be avoided by the process of the present invention. Accordingly, it is an object of this invention to provide a hydroforming process which is not limited in potential octane improvement by the presence of n-paraffins in the feed. It is also an object of this invention to provide a hydroforming process wherein the n-paraffins are converted without the need of additional process equipment. Still another object of this invention is to provide a hydroforming process wherein the yield of propane is maximized.

In accordance with this invention, the foregoing and other objects are accomplished by placing a selective hydrocracking catalyst comprising hydrogen-erionite in the bottom of the lead reactor of a fixed-bed hydroforming process. A preheated hydrocarbon fraction boiling in the motor fuel or naphtha range is then passed downwardly through the bed. The feed first contacts a conventional hydroforming catalyst and then the selective hydrocracking catalyst. The amount of conventional hydroforming catalyst in the lead reactor will be sufficient to allow the desired degree of dehydrogenation to take place and to permit the feed to cool to the desired hydrocracking conditions. The amount of selective hydrocracking catalyst in the bottom of the lead reactor will be sufficient to permit cracking of a substantial part of the nparaffius in the feed.

DETAILED DESCRIPTION The hydrocarbon fractions which may be treated by the process of the present invention are those which are conventionally employed in hydroforming operations. In general, these are naphtha fractions boiling within the range of 60 to 450 F. and include the heavy naphthas boiling within the range of 200 to 450 F. and the light naphthas boiling within the range of to 300 F. A preferred feedstock is a gasoline fraction having an initial boiling point between about 100 and 250 F. and a final boiling point between about 350 and 450 F. The feedstocks used in the present invention will contain between about 15 and 45 wt. percent n-paraffins having chain lengths between about six and 12 carbon atoms.

The process of the present invention will be carried out in a multiple-stage reaction train having at least two stages. It will be understood, however, that only the first or lead reactor will contain both a hydroforming and selective hydrocracking catalyst. The remaining stages will be operated as though the process were a conventional, fixed-bed, multistage hydroforming process.

In the present invention the feed is preheated to a temperature within the range of about 750 to l,l50 F., preferably within the range of 850 to 950 F. The feedstock is then passed downwardly through the lead reactor.

The upper portion of the lead reactor will contain a conventional hydroforming catalyst. Such catalysts are well-known in the art, and include the oxides and sulfides of the metals of ,Groups 1V, V, VI, VII and VIII of the Periodic Table of the Elements. These catalysts may be used directly or on a suitable support, such as alumina gel, precipitated alumina, zincalumina spinel, chromia-alumina, silica-alumina, etc., in general, any porous material having a pore size of at least 6 Angstroms. The molybdena-alumina and platinum-alumina catalysts are preferred in the present invention. The platinumalumina catalyst is particularly preferred.

The lower portion of the lead reactor will contain a selective hydrocracking catalyst comprising a metallic hydrogenation component in combination with the hydrogen form of erionite. Suitable hydrogenation components include the metals and the oxides of the metals of Groups V-B, VI-B, VIIB or VIII of the Periodic Table; e.g., cobalt, nickel, tungsten, platinum, palladium, etc. The platinum group metals are preferred.

Erionite is a naturally occurring crystalline aluminosilicate zeolite having elliptical pore openings of about 4.7 to 5.2 Angstroms on its major axis. Erionite is represented chemically by the formula:

in its dehydrated form. Synthetic erionite can be prepared by methods known in the art, such as those disclosed in US. Pat. No. 2,950,952 and copending application Ser. No. 532,056, which was filed on Mar. 7, 1966. The synthetic form of erionite is characterized by pore openings of about 5 Angstrom units and differs from the naturally occurring form in its potassium content and the absence of extraneous metals.

The hydrogen form of erionite is obtained by replacing at least 75 percent of the potassium ion with hydrogen so as to obtain a product having less than 3 wt. percent potassium. This may be accomplished by contacting the erionite with an aqueous solution of an ammonium salt and thereafter heating to convert the ammonium ion to the hydrogen ion.

Incorporation of the hydrogenation component with the hydrogen-erionite may be accomplished by any of the methods known in the art, such as ion exchange, impregnation, etc. [on exchange is preferred in the present invention. Moreover, when palladium is employed as the hydrogenation component, it is preferred that the erionite be exchanged with an ammoniacal solution of palladium chloride and then dried and calcined at a temperature between 800 to l,0O F. The amount of hydrogenation component may range from about 0.1 to about 25 wt. percent based on the weight of final product. In the case of the platinum group metals, e.g., platinum and palladium, the preferred amount will be in the range of about 0.1 to 6 wt. percent, and more preferably from about 0.5 to 3 wt. percent, based on dry catalyst.

The feedstock will be passed over both the hydroforming catalyst and the selective hydrocracking catalyst at a rate between about 0.2 and I0 v./v./hr., most preferably at a rate between 1 to 3 v./v./hr. Hydrogen will be supplied to the reactor at a rate between 2,000 to [0,000 SCF/bbl. feed, and preferably at a rate of 4,000 to 10,000 SCF/bbl. In general, the hydroforming catalyst will comprise about 25 to 75 wt. percent of the fixed catalyst bed in the first reactor. The selective hydrocracking catalyst will comprise the remaining 75 to 25 wt. percent.

The amount of hydroforming catalyst in the lead reactor will be sufficient to permit the feed temperature to decrease to the desired hydrocracking temperature. It will be understood that the reduction in feed temperature will be due in part to heat loss, but primarily to the heat of reaction during reforming. In general, the hydrocracking temperature will be in the range of 750 to 900 F., and preferably 825 to 875 F. Temperatures in this range are preferred because these temperatures yield an optimum balance between overall n-paraffin conversion and propane yield, on the one hand, and hydrogen yield on the other hand. Hydrogen yield may or may not be important of itself. depending on local economies. However, selective hydrocracking of n-paraffins consumes hydrogen, reducing the hydrogen partial pressure in the recycle gas, in turn reducing hydrogen partial pressure in the reactor, and in turn tending to cause more rapid deactivation of the catalysts, particularly the hydroforming catalyst. To offset this effect, temperatures must be reduced to maintain a given cycle length, tending to reduce the capability of the entire reactor system. It is found, however, that the selective hydrocracking catalyst consumes less hydrogen, per unit weight of n-paraffins cracked, at lower temperatures. This behavior tends to make low hydrocracking temperatures desirable, but the fact that cracking activity increases with temperature tends to make high temperatures desirable. Thus, an optimum hydrocracking temperature of roughly 850 F. is found as a result of these opposing tendencies.

It should be noted that the selective hydrocracking catalyst used in the present invention may be subjected to water vapor, chlorine and/or chlorides, and regeneration gases required for the hydroforming catalyst. Accordingly, it is essential that the hydrocracking catalyst exhibit at least some degree of stability to these conditions. Of the selective hydrocracking catalysts known in the art, hydrogen erionite is the only one which exhibits any appreciable degree of such stability.

It will be understood that it will be necessary to remove carbon deposits from the hydrogen-erionite hydrocracking catalyst periodically. This can be accomplished by any of the processes known in the art, such as burning. This can, of course, be accomplished without adversely affecting the hydroforming catalyst.

it will be understood that any number of hydroforming stages can be used to effect the desired improvement; however, three or four is generally sufficient and is preferred. The hydrocarbon fraction will be preheated to a temperature between 750 to l,l50 F., and preferably between 900 to l ,000 F before each of the subsequent hydroforming stages.

The C, and lighter components may be used directly as a fuel, or may be further fractionated to obtain high-quality propane and/or butane streams. The product from the final hydroforming stage will exhibit an improved octane rating due to the removal of the n-paraffins and conversion of naphthenes, etc. The final stage product may be used as a motor fuel.

PREFERRED EMBODIMENT The present invention is illustrated, but in no way limited, by the following examples. A preferred embodiment is illustrated by example 3. EXAMPLE I A naphtha fraction boiling between 200 and 3l0 F. and containing 32 wt. percent n-paraffins was preheated to 903 F. This feed, along with 7,500 SCF/bbl. of hydrogen, was then passed downwardly through the lead reactor of a fixed-bed, multistage hydroforming process. The top portion of the lead reactor contained a platinum-alumina hydroforming catalyst which contained 0.6 wt. percent platinum based on dry catalyst. The feed was passed over the hydroforming catalyst at a rate of L45 w./h./w. The lower portion of the lead reactor contained a selective hydrocracking catalyst comprising 05 wt. percent PD on hydrogen erionite. The catalyst was prepared by ion-exchanging the synthetic erionite with NH,NO;, solution so as to replace substantially all the Na and 75 percent of the potassium with Nl-l,+. The temperature of the hydrocracking section of the reactor was 825 F. The flow rate over the hydrocracking catalyst was about 23 w./h./w.

The effluent from the lead reactor was passed to additional stages. Before each stage, the effluent was preheated to 890 to 900 F. Each of the additional stages contained a platinumalumina hydroforming catalyst of the same composition as that used in the lead reactor as the sole catalyst.

As a result of the hydrocracking reaction, about 20 percent of the n-paraffins in the feed were converted to C, and lighter components. The composition of the C and lighter components product is set forth in the table below:

TABLE I Results of Example 1 Component Wt. X: in C, and Lighter Product i on Feed C, 8.3 C,, wt. i L C l3.0 C,. wt. in 3.70 C 37.2 C,, wt. '5: 10.32 C, 24.7 C wt. *1 8.20 C 16.8 C,*, vol. 5% 7 l .0

The hydrogen consumption due to the cracking reaction was about 0.39 wt. percent.

The product from the final stage had an octane number of 92 as compared to 38.5, which was the octane number of the feed.

EXAMPLE 2 This run was completed in the manner set forth in example 1, except that the lead reactor feed was preheated to 899 F. and the temperature in the hydrocracking section was 830 F. The results obtained are shown below.

The hydrogen consumption due to the cracking reaction was 0.45 wt. percent. The octane number of the final stage product was 96.

EXAMPLE 3 This run was also completed in the manner set forth in example 1, except that the lead reactor feed was preheated to 934 F. and the temperature of the hydrocracking section was 860 F. The results obtained are shown below.

The hydrogen consumption due to the cracking reaction was 0.54 wt. percent. The octane number of the final stage product was 98.1.

The results obtained in examples I through 3 clearly show that the n-paraffins in the feed can be substantially completely converted to lighter hydrocarbons. These data also show that by variations in the hydrocracking temperature, the propane yield can be maximized.

Having thus described and illustrated the present invention. what is claimed and sought to be protected by Letters Patent is:

I. An improved hydroforming process comprising the steps of:

a. preheating a hydrocarbon fraction boiling within the range of 50 to 450 F. to a temperature between 750 to l 1 50 F b. passing said preheated hydrocarbon fraction downwardly through a fixed bed of catalyst, said fixed bed of catalyst comprising a hydroforming catalyst in its upper portion and a selective hydrocracking catalyst comprising hydrogen erionite in its lower portion;

c. preheating the effluent from the first reactor to a temperature between 750 to F.;

d. passing said preheated effluent over at least one additional fixed bed of hydroforming catalyst; and

e. recovering a product having an improved octane rating from the final stage.

2. An improved process according to claim I wherein the selective hydrocracking catalyst comprises a platinum group metal in combination with said hydrogen-erionite.

3. An improved process according to claim 1 wherein the fixed-bed of catalyst in the lead reactor comprises from 25 to 75 wt. percent of a hydrofonning catalyst in its upper portion and from 75 to 25 wt. percent of said selective hydrocracking catalyst in its lower portion.

4. An improved process according to claim 1 wherein the hydroforming catalyst in the lead reactor comprises a metal oxide or metal sulfide of a metal selected from Groups IV. V, VI, VII and Vlll of the Periodic Table of the Elements.

5. The process of claim 1 wherein the temperature of the hydrocracking reaction is between and F.

t i i i 

2. An improved process According to claim 1 wherein the selective hydrocracking catalyst comprises a platinum group metal in combination with said hydrogen-erionite.
 3. An improved process according to claim 1 wherein the fixed-bed of catalyst in the lead reactor comprises from 25 to 75 wt. percent of a hydroforming catalyst in its upper portion and from 75 to 25 wt. percent of said selective hydrocracking catalyst in its lower portion.
 4. An improved process according to claim 1 wherein the hydroforming catalyst in the lead reactor comprises a metal oxide or metal sulfide of a metal selected from Groups IV, V, VI, VII and VIII of the Periodic Table of the Elements.
 5. The process of claim 1 wherein the temperature of the hydrocracking reaction is between and F. 